Autotrophic denitrification of high-salinity wastewater using elemental sulfur: batch tests

The feasibility of autotrophic denitrification of a high-salinity wastewater using sulfur-oxidizing autotrophic denitrificants was studied. These autotrophic bacteria oxidize elemental sulfur to sulfate while reducing nitrate to elemental nitrogen gas, thereby eliminating the need for the addition of organic carbon compounds. A series of bench-scale batch tests was performed with synthetic and actual flue gas desulfurization (FGD) wastewater to examine the effects of various environmental and operational factors such as temperature, pH, high salinity, and potentially toxic substances on the rate of autotrophic denitrification using elemental sulfur. Specific denitrification rates of 6 to 8 mg nitrate-nitrogen (NO3- -N)/g volatile suspended solids (VSS) x h were obtained. The highest denitrification rates were found between pH 7.0 and 8.0 and a temperature of 30 degrees C. The denitrification rate started to decrease above an osmotic pressure of 19 atm (approximately 70% of seawater), independent of the type of salt ions, and amounted to approximately 70% activity at the concentration of seawater. Polyphosphate or pyrophosphate could be used as the source of phosphorus instead of orthophosphate because the latter caused immediate calcium phosphate precipitation in the FGD wastewater. Inhibiting factors attributed to inorganic or organic compounds originating from coal combustion were discussed.